The present invention relates to an air conditioner, a refrigerator, and so forth, and, more particularly, it is concerned with improvement in a plate-fin-tube type heat exchanging device to be used for these apparatuses.
In general, the plate-fin-tube type heat exchanging device is of such a construction that a plurality of heat transmission tubes are passed through a plurality of juxtaposed plate fins in the direction perpendicular to these plate fins, and the heat transmission tubes are held in close contact with the fins by tube expansion, or various other expedients. The primary fluid such as cool or warm water, refrigerant, or the like is caused to pass through these heat transmission tubes, while the secondary fluid such as air, etc. is caused to pass through the space among these fins, thereby effecting the heat exchange between these two fluids.
Incidentally, there tends to be readily formed a boundary layer of flow in the air stream flowing along and through these fins. The temperature gradient in this boundary layer is so large that this layer portion constitutes enormous heat resistance. Further, this boundary layer grows up thick in the flowing direction of the secondary fluid, on account of which the heat transfer rate of the fins is considerably lowered at the downstream part of the fins in the fluid flowing direction.
Thus, with the plate-fin tube type heat exchanger, the most significant problem is the low heat transfer rate at the side of the secondary fluid (the fin side). In order therefore to improve this heat transfer rate at the fin side, it is necessary to effectively prevent the abovementioned boundary layer from forming and growing up, for which purpose there have so far been made various proposals concerning the shape of the fins to be worked on the surface of the plate fin.
In the following, explanations will be made as to a conventional example of the plate-fin-tube type heat exchanger when it is assembled in an air conditioning apparatus, in reference to FIGS. 1 and 2 of the accompanying drawing which are respectively a perspective view showing a construction of a room unit of a separate type air conditioning apparatus and a schematic cross-sectional view of the room unit of such separate type air conditioning apparatus.
In the drawing, a reference numeral 12 designates a main body of the air conditioner; a numeral 13 refers to a front panel to cover the front face of the main body of the air conditioner, having an intake grill 14 and an air outlet 15 formed therein; a reference numeral 16 denotes a casing which forms an air course 17 to communicatively connect the intake grill 14 and the air outlet 15 within the main body 12; a numeral 18 refers to an air blower installed at the side of the air outlet 15 of the air course; and a reference numeral 100 designates the plate-fin-tube type heat exchanger installed at the side of the intake grill 14 in the air course 17 and having a drain pan 19 provided underside of it.
In the illustrated air conditioning apparatus, the air flows in the direction as shown with arrow marks. That is to say, with rotation of the air blower 18, the air flows into the plate-fin-tube type heat exchanger 100, the heat exchanging characteristic of which is largely governed by the quantity of this air flow taken into the heat exchanger.
FIG. 3 of the accompanying drawing is an exploded perspective view showing a construction of an outside unit of the separate type air conditioning apparatus. In the drawing, a reference numeral 20 designates a main body of the outside unit; a reference numeral 21 indicates a partition plate to divide the main body 20 into a heat exchanger room 22 and a compressor room 23; numerals 24 and 25 refer to a left side plate and a right side plate of the main body 20, respectively; a reference numeral 26 represents a cover plate in an inverted L-shape for covering the top and front faces of the main body 20 and having an air outlet formed in the front side (incidentally, the air inlets (not shown in the drawing) being formed in the left side plate 24 and the back side of the main body 20); a reference numeral 28 designates a compressor installed in the compressor room 23. An L-shaped, plate-fin-tube type heat exchanger 100 is disposed in confrontation to the above-mentioned left side plate 24 and the back side of the main body 20, and is communicatively connected with the compressor 28 by means of a tube 29. A numeral 30 refers to a bracket for attaching an air blower (not shown) thereto in the direction of the air outlet 27.
In the illustrated air conditioning apparatus, the air flows in the direction as shown with arrow marks. That is to say, with rotation of the air blower (not shown), the air flows into the plate-fin-tube type heat exchanger 100 through the air inlets (not shown) and is discharged from the air outlet 27. The heat exchanging characteristic of this heat exchanger is largely governed by the quantity of the air taken into this heat exchanger.
FIGS. 4, 5 and 6 of the accompanying drawing illustrate one example of a conventional plate-fin-tube type heat exchanger to be incorporated in an air conditioning apparatus of a general type, which is disclosed in unexamined Japanese utility model publication No. 144988/1981. As shown in FIG. 4, the plate-fin-tube type heat exchanger is constructed with a plurality of fins 1 arranged in parallel with one another at a certain definite space interval among them and a plurality of heat transmission tubes 2 passed through these fins at the right angle. Air flows through the space among these fins 1 in the arrow direction, during which the heat exchange is effected between the air current and the fluid in the heat transmission tubes 2.
FIG. 5 is a front view of the conventional plate-fin-tube type heat exchanger, and FIG. 6 is a cross-sectional view of the heat exchanger taken along a line VI--VI in FIG. 5. As seen from the drawing, a plurality of incisions or cuts are made in the planar fin base plate 1 having a plurality of holes 3 formed therein for passing the heat transmission tubes (not shown) therethrough. The incisions are made at a space in the plate fin between the adjacent tube inserting holes 3 arranged in the longitudinal direction of the fins, through which the heat transmission tubes (not shown) are passed, and in the direction orthogonally intersecting with the flowing direction of the fluid passing through the space intervals among the fin base plates 1. Then, the incised portions are jerked up toward both front and rear surfaces of the fin base plate 1 followed by bending both edges inwardly toward the surface of the fin base plate in a parallel relationship therewith, thereby forming a plurality of cut and raised pieces 4 or louvers arranged in a certain definite direction and in parallel with the longitudinal direction of the fin base plate 1.
The purpose of the proposal in this prior art is to improve the heat transmission characteristic in the known heat exchanger. However, with such construction of the fins as mentioned above, a temperature field of the boundary layer to be formed by the cut and raised pieces 4 at the upstream side of the air flow (shown in the arrow mark) gives influence on the cut and raised pieces 4 at the downstream side of the air flow, which brings about various disadvantages such that the leading edge effect of these cut and raised pieces at the downstream side cannot be fully made use of; the heat transfer rate is conversely low, the wind pressure loss increases; and the drive power for air blowing becomes large, and others. There is also a problem from the aspect of working of the fin such that, since the cut and raised pieces are all formed in one and the same direction with respect to the fin base plate, distortion would occur in the fin base plate as a whole during the working of the fins.